This invention relates to apparatus and methods for automatically monitoring and adjusting manufacturing processes, for example, processes which produce an ongoing stream of outputs such as discrete absorbent articles, for example disposable diapers, effective to absorb body fluids. Such absorbent article products are typically fabricated as a sequence of work pieces being continuously processed on a continuous web and/or continuous processing line of fabrication and assembly machines.
Such absorbent article product generally comprises an absorbent core confined between a moisture impervious baffle of e.g. polyethylene and a moisture pervious body side liner of e.g. non-woven fibrous material. The absorbent articles are typically made by advancing a web of either baffle or body side liner material along a longitudinally extending path, applying the absorbent core to the advancing web, and then applying the second web over the combination of the advancing web and the absorbent core. Other elements such as elastics, leg cuffs, containment flaps, waste bands, and the like are added as desired for the particular product being manufactured, either before, during, or after, applying the second web. Such elements may be oriented longitudinally along the path, or transverse to the path, or may be orientation neutral. As added, such other elements are typically registered on the absorbent article in one or both of the with machine direction and the cross machine direction.
Typical such manufacturing processes are designed to operate at steady state at a pre-determined set of operating conditions. A typical such process has a beginning and an end, and has a start-up period corresponding with the beginning of the operation of the process and a shut-down period corresponding with the end of the operation of the process. The start-up period of the process generally extends from the initiation of the process to the time the process reaches specified steady state conditions. The shut-down period of the operation generally extends from the time the process leaves steady state conditions to the termination of operation of the process.
While the process is operating at steady state conditions, the result desired from the process Is desirably and typically achieved. For example, where the process is designed to produce a certain manufactured good such as disposable diapers, acceptable manufactured goods are normally produced when the process is operating at specified steady state conditions.
As used herein, xe2x80x9csteady statexe2x80x9d conditions represents more than a single specific set of process conditions. Namely, xe2x80x9csteady statexe2x80x9d represents a range of specified process conditions which correspond with a high probability that acceptable goods will be produced, namely that the products produced will correspond with specified product parameters.
Known statistical models and control models for controlling the manufacturing process are based on assumptions that the goods produced during operation of a given such process represent a single homogeneous population of goods. The focus of such statistical models and control models is based on steady state conditions.
However, actual operation of many manufacturing processes, including highly automated processes, typically includes the occurrence of periodic, and in some cases numerous, destabilizing events. A xe2x80x9cdestabilizing eventxe2x80x9d is any event which upsets, interferes with, or otherwise destabilizes the ongoing steady state characteristics of either process parameters or unit-to-unit product parameters. A typical such destabilizing event is one which either causes unacceptable product to be made, or which causes the process controller to recognize and/or report an anomalous process condition, or both.
A typical manufacturing automatic process control system can make adjustments to the process in real time based on horizontal analysis such as averaged data collected from a pre-determined quantity, e.g. a predetermined number of serially-arranged units of work pieces currently being processed. In addition, such typical manufacturing automatic process control system can automatically cull product according to predetermined criteria upon the occurrence of a pre-defined triggering event that e.g. inherently produces at least a minimum quantity of defective product. Thus, depending on the nature and severity of a given destabilizing event, the process controller may respond to the destabilizing event by culling product and/or by making adjustments to one or more process conditions, for example, shutting down the operation, speeding up or slowing down the operation, changing one or more of the other operating parameters, sounding an alarm to alert an operator, or the like.
Upon the occurrence of such destabilizing events, the data representing products fabricated by such manufacturing operation may begin moving away from target conditions whereupon corrective action should be taken in the manufacturing operation; or the data may move outside acceptable specifications whereby the respective units of product should be culled from the product stream. However, such control systems typically collect a number of data points from sequentially arranged units of product in the stream of goods being produced, and compute a data average, before taking corrective action. In the meantime, defective product may be produced, and may subsequently be packaged for shipment.
A variety of possible events in the manufacturing operation can cause the production of absorbent articles which fall outside the specification range. For example, stretchable materials can be stretched less than, or more than, desired. Elements can become misaligned relative to correct registration in the manufacturing operation. Timing between process steps, or speed of advance of an element, can become out-of-tolerance. If such non-catastrophic deviations in process conditions can be detected quickly enough after the deviation from target begins to show up in the product, typically process corrections can be made, and the variances from target conditions can accordingly be reduced, without having to shut down the manufacturing operation and without having to cull, and thereby waste, product.
In some cases, the changes are so severe, or happen so quickly, that process corrections based on such anomalies detected in the product concurrently being produced are insufficient to avoid production of defective product which must be culled.
Further, where the anomalous condition is inherently temporary and short term, by the time automatic corrective action based on currently collected anomalous data, namely horizontal analysis, can be implemented, the temporary time period during which the anomalous behavior occurs may have expired. In such event, the corrective action is applied to non-defective work pieces, risking the possibility of creating defective work pieces that would have, but for the corrective action, been within acceptable specifications.
Exemplary of destabilizing events of interest in the invention are, for example, splices in any of the several materials being fed into the process, web breaks, defective zones in an input material, the start-up period, the shut-down period, unplanned start-up and unplanned shut-down periods, and the like. Typical responses to such more drastic anomalous destabilizing events might be culling product from the manufacturing line, sending one or more corrective control commands to control actuators on the process line, sounding an alarm, slowing down the processing line, shutting down the process line, and the like.
A variety of automatic product inspection systems are available for routine ongoing automatic inspection of product being produced on a manufacturing line and for periodically and automatically taking samples for back-up manual evaluation. Indeed, periodic manual inspection of product samples is still important as a final assurance that quality product is being produced.
Where the process produces product wherein one or more elements is mis-registered on The product, early correction of the defective mis-registration is highly desirable in order to minimize the amount of defective product which is produced. While existing control systems can detect mis-registration, such control systems take action only after collecting enough sample data points from sequentially-arranged units of product to develop a reliable average for the registration data. Moreover, where the mis-registration characteristic represents a rapidly changing parameter such as at start-up, at shut-down, or at a splice, the calculated average is of limited value until the parameter of interest becomes relatively stable. Yet further, known control systems are powerless to predict the degree and direction of mis-registration, or to take any pro-active corrective action with respect to such mis-registration. Rather, such systems rely on first collecting data from the currently and sequentially mis-registered product, and averaging the respective data, by which time the units of product, used to generate the data, may have exited the manufacturing process.
Body fluid absorbing personal care absorbent articles such as are of interest herein for implementation of the invention are typically manufactured at speeds of about 50 to about 1200 articles per minute on a given manufacturing line. Preferred speeds are between about 300 and about 1000 articles or other units of product per minute. Accordingly, it is impossible for an operator to manually inspect each and every article so produced.
A significant problem with known control systems is that they are designed for and focused on making process adjustments based on horizontal analysis, namely calculating a representative parameter based on data collected from a sample of units of product arranged in sequence on the production line, and subsequently generating corrective instructions to the production line machines, based on the calculated representative parameters. Such conventional control systems do not take into account certain predictive characteristics regarding specific product segments, or units of product, which can be gleaned for each unit of product based on its relationship to a destabilizing event.
As a result, while existing statistical control models may be rather efficient at identifying and culling defective product resulting from random or unpredictable anomalous conditions in the process, or resulting from a minor deviation from steady state conditions, when the process experiences a destabilizing event, known statistical control models are unable to anticipate or predict, and correct for, defective product characteristics based on past product behavior corresponding to respective such destabilizing events. By corollary, such control models are unable to take corrective action until off-target product is in fact produced, and recognized as being off target.
Thus, known statistical control models are, for example, unable to adjust registration at start-up based on mis-registration which occurred during a previous start-up.
It is an object of this invention to provide a method of pro-actively making process parameter adjustments, such as registration adjustments, upon occurrence of a destabilizing event.
It is another object to make such process adjustments based on historical data collected during one or more previously-occurring such destabilizing events.
It is still another object to make such adjustments specific to individual units of the product, e.g. individual work pieces, based on the amount of mis-registration recorded for the individual units of product in respective previously-occurring such destabilizing events.
It is a further object to issue corrective adjustment commands before any defective product is produced.
Still another object is to collect data, and generate a deviation profile for one or more parameters representative of the effect of a respective destabilizing event.
Yet another object is to modify the deviation profile and to thereby create a correction profile element from the deviation profile, for the given type of destabilizing event.
A still further object is to invert the deviation profile, and to modify the inverted deviation profile in developing the correction profile element, and accordingly a new correction profile.
A further object is to apply the correction profile to a subsequent occurrence of the type destabilizing event for which the data was collected and averaged.
A further object is, while applying the correction profile, sensing and recording new registration deviation data resulting from application of the correction profile.
Other objects are achieved in, after recording the new registration deviation profile, inverting the new deviation profile to thereby develop a new correction profile element, and applying the new correction profile element to the existing correction profile, thus to create a new, next generation correction profile which takes into account the deviations used in developing the correction profile element.
Yet other objects are obtained by, upon occurrence of such pre-defined destabilizing event, applying the then current correction profile, and sensing and recording a corresponding registration deviation profile pertaining to the respective current destabilizing event; and periodically incorporating adjustments into the correction profile based on the registration deviations recorded from previous such destabilizing events.
This invention contemplates a method of controlling a process producing segments of product and wherein a destabilizing event of a particular type periodically destabilizes the process, resulting in a deviation from a target parameter in a number of segments of the product, from segment number 1 to segment number n. The method comprises upon occurrence of the particular type of destabilizing event, associating with respective ones of the n segments of product, deviation amounts corresponding to historical deviation amounts for the respective so-numbered units of product in past occurrences of the particular type of destabilizing event; and applying to selected ones of the n units of product, correction factors derived from respective associated historical deviation amounts for the respective nth units of product, thereby making pro-active adjustments to respective ones of the n units of product, upon occurrence of the destabilizing event.
Preferred methods include applying the correction factors to each of the n units of product.
In exemplary embodiments, the method includes applying the correction factors as registration factors, to either or both of with machine direction registration and cross machine direction registration.
In preferred embodiments, the method includes, using a computing controller, computing correction factors for selected units, optionally uniformly spaced units, or each unit, using historical operating data from at least two previous occurrences of the destabilizing event and respectively developing a correction profile using the combination of the correction factors, for use upon occurrence of a future destabilizing event.
The method preferably includes computing separate and distinct correction factors for selected units, optionally uniformly spaced units, or each unit, to which such registration correction factor is to be applied, including deriving such correction factor from the same numbered nth unit in the previous destabilizing event or events, whereby each such correction factor is based on data derived from the respective nth unit of product past the destabilizing event, in such previous destabilizing event or events.
Preferably, the method is applied to a manufacturing process producing discrete units of absorbent article product for personal care use in absorbing body exudates.
Preferred embodiments of the invention include collecting deviation information from ones of the respective n units of product during subsequent occurrences of the destabilizing event and, based on the deviation information so collected, periodically making adjustments to the correction profile and applying the adjusted correction profile to ones of the respective n units of product at future occurrences of the destabilizing event.
In some embodiments, the method includes collecting and recording registration data for respective ones of the subsequent n units of product, and thereby obtaining fresh registration deviation data on multiple units of product, up to n units, for the destabilizing event, thus obtaining samples for up to n units of product, for respective ones of the n units of product, using the computing controller, automatically in real time computing a representative registration deviation based on the sample obtained for the respective nth unit of product, and thereby obtaining a registration deviation profile representative of the respective units of product associated with the respective destabilizing event, combining and/or modifying up to 10, in some cases up to 20 or more, of the deviation profiles, and thereby obtaining a representative composite correction profile up-date element for such type destabilizing event, upon obtaining the correction profile up-date element, adding the so-obtained correction profile up-date element to the registration correction profile, thus to obtain an up-dated registration correction profile, and applying the up-dated registration correction profile to a subsequent occurrence of the respective type destabilizing event, preferably including beginning to add the so-obtained correction profile up-date element to the correction profile no later than the n+20th unit, more preferably no more than the n+10th unit, of the last destabilizing event from which the correction profile element data was derived.
In other embodiments, the method includes collecting and recording registration data for respective ones of the subsequent n units of product, and thereby obtaining fresh registration deviation data on multiple units of product, up to n units, for the destabilizing event, thus obtaining samples for up to n units of product, for respective ones of the n units of product, using the computing controller automatically in real time computing a representative registration deviation based on the sample obtained for the respective nth unit of product, and thereby obtaining a registration deviation profile representative of the respective units of product associated with the respective destabilizing event, combining and/or modifying the deviation profile, and thereby obtaining a representative correction profile up-date element for such type destabilizing event, upon obtaining the correction profile update element, beginning to add the so-obtained correction profile up-date element to the registration correction profile, no later than the 2 nth unit of the last destabilizing event from which the correction profile element data was derived, thus to obtain an up-dated registration correction profile, and applying the up-dated registration correction profile to a subsequent occurrence of the respective type destabilizing event.
In a second family of embodiments, the invention contemplates a method of controlling a process producing discrete units of absorbent article product for personal care use and wherein a destabilizing event of a particular type periodically destabilizes the process, resulting in a deviation from a target parameter in a number of units of the product, from unit number 1 to unit number n. The method comprises operating the process, including continuing to operate the process upon occurrence of such type destabilizing events, x times, x being greater than 1, and upon occurrence of such destabilizing events, collecting and recording product data for respective ones of the subsequent n units of product, and thereby obtaining product deviation information on multiple units of product, up to n units of product, for each of the x such destabilizing events, thus obtaining up to x samples for each of the n units of product; for respective ones of the n units of product, computing a representative product deviation based on the samples obtained for the respective nth unit of product, from the x such destabilizing events, and thereby obtaining a product deviation profile representative of the product deviations of the respective units of product from a target parameter, and obtained from the x destabilizing events; modifying the deviation profile, and thereby obtaining a product correction profile element for such type destabilizing event, the correction profile including a correction for each of the n units of product for which a product deviation indication was obtained; adding the so-obtained product correction profile to any pre-existing product correction profile used in collecting the sample, thus to obtain an up-dated product correction profile; and applying the up-dated product correction profile to a subsequent occurrence of the respective type destabilizing event.
In preferred embodiments, the method includes, while applying the up-dated product correction profile to a subsequent such destabilizing event, collecting product deviation data for up to respective n units of product, and using the so-collected deviation data to further up-date the product correction profile, for example by computing of the product deviations by averaging the deviations recorded for the respective nth units of product or work pieces.
The method may include collecting product deviation information from ones of the respective n units of product during subsequent occurrences of the destabilizing event, and periodically making adjustments to the product correction profile based on the product deviation information so collected.
Yet another family of embodiments comprehends a method of controlling a process producing product in discrete product segments. The method comprises operating the process, including continuing to operate the process upon occurrence of a destabilizing event, and collecting and recording process performance data for respective ones of the subsequent n units of product, and thereby obtaining process performance deviation information on multiple units of product, up to n units of product, for such destabilizing event, thus obtaining samples of the performance data for up to the n units of product; for respective ones of the n units of product, computing a representative performance deviation based on the sample obtained for the respective unit of product, and thereby obtaining a process performance deviation profile representative of the respective units of product; modifying the deviation profile, and thereby obtaining a process performance correction profile element for the destabilizing event, including correction for each of the n units of product for which a process performance deviation indication was obtained; incorporating the so-obtained performance correction profile element into any pre-existing correction profile used in collecting the samples, thus to obtain an up-dated performance correction profile; and applying the up-dated performance correction profile to a subsequent occurrence of respective type destabilizing event.
In preferred embodiments, the method includes applying the performance correction profile to each of the n units of product.
The invention yet further comprehends apparatus for controlling a process producing segments of product and wherein a destabilizing event of a particular type periodically destabilizes the process, resulting in a deviation from a target parameter in a number of segments of the product, from segment number 1 to segment number n. The apparatus comprises a manufacturing line comprising a plurality of machines manufacturing the product; a computing controller effective, upon occurrence of the particular type of destabilizing event, to associate with respective ones of the n segments of product, deviation amounts corresponding to historical deviation amounts for the respective so-numbered units of product in past occurrences of the particular type of destabilizing event, and to apply to respective nth ones of the n units of product, correction factors derived from respective associated historical deviation amounts for the respective nth units of product; one or more detection devices detecting one or more parameters with respect to the process or product being produced by the process; and one or more actuation devices effecting adjustments to the machines in response to the correction factors developed from deviation amounts detected in one or more previous destabilizing events, thereby to make pro-active adjustments to respective ones of the n units of product, upon occurrence of the destabilizing event.